The present invention pertains to an accumulation technique and a conveyor system utilizing the accumulation technique. The invention may be applied to an individual accumulation conveyor line or to a conveyor system made up of a plurality of accumulation conveyor lines having outputs merged at a merge assembly.
It is known to provide accumulation capability in conveyor systems in order to accommodate uneven throughput of articles in the system. For example, a conveyor system may receive articles on conveyor lines fed from loading doors in which trucks or other containers are discharged of articles at the loading doors. Some loading doors may be receiving articles, while others are not. Likewise, the conveyor system may be applied to a manual pick operation in which totes or other containers of articles are received along various conveyor lines at various intervals and are supplied to a downstream process. The rate of input of articles to the conveyor lines may be uneven. It is desirable to provide accumulation of articles along the conveyor lines. The conveyor lines may supply a merge assembly in order to combine the outputs of the conveyor lines prior to supplying articles to a downstream process, such as sortation system.
Two general types of accumulation conveyors are known. One type of accumulation conveyor accumulates articles behind a stop until the accumulation conveyor is full, at which time articles are discharges, in turn, to the merge assembly. The difficulty with this type of accumulation conveyor is that it produces line pressure on the upstream articles. The line pressure may be sufficient to dislodge articles from the line of articles, thereby causing side-by-side articles, which are difficult to sort. This is especially problematic for small articles being accumulated.
Another type of accumulation conveyor is a zero-line-pressure, or non-contact, accumulation conveyor. In such accumulation conveyor, the individual articles are accumulated individually in zones in order to avoid applying line pressure to downstream articles. While such zero-line-pressure accumulation conveyor avoids the difficulty of build-up of line pressure, it is common to have no more than one article per zone. Gaps are introduced between the articles during accumulation especially where a wide variety of article sizes are being handled by the conveyor system. The gaps reduce the throughput of the system because they reduce the number of articles that may be handled by each given length of conveyor at any given time.
Both of the known types of accumulation conveyors suffer from complexity and expense. To the extent that accumulation of articles is required, the entire length of the conveying line requiring accumulation is made up of an accumulation apparatus.
Accumulation conveyors have traditionally been pneumatically operated or a combination of electrically driven and pneumatically actuated systems. It would be desirable to overcome the high installed cost of such traditional accumulation conveyors and to overcome other difficulties associated with such traditional accumulation conveyors by utilizing an all-electrically operated system made up of motorized roller zone conveyors in the accumulation conveyor. This advantageously eliminates the need for supply of pneumatic source to the accumulation conveyor as well as provides other beneficial features to the accumulation conveyor. One difficulty with using motorized roller zone conveyors is that repeated cycling of the motorized roller on and off within a relatively short cycle time can result in the build-up of undesirable heat within the motorized roller. Therefore, it is desirable to reduce the number of times that a motorized roller-bases accumulation conveyor zone conveyor cycles on and off during an accumulation cycle.